Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Options
Options, Beginning Balance	7,669,553
Options, Granted	1,838,073	3,669,958
Options, Forfeited	(713,754)
Options, Exercised	(1,674,905)
Options, Ending Balance	7,118,967		7,669,553
Options, Vested and expected to vest	5,588,472
Options, Exercisable	2,932,418
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning Balance	$ 4.08
Weighted Average Exercise Price, Granted	$ 16.66
Weighted Average Exercise Price, Forfeited	$ 5.94
Weighted Average Exercise Price, Exercised	$ 3.48
Weighted Average Exercise Price, Ending Balance	$ 7.29		$ 4.08
Weighted Average Exercise Price, Vested and expected to vest	$ 6.32
Weighted Average Exercise Price, Exercisable	$ 4.02
Average Intrinsic Value/Weighted Average Exercise Term
Average Intrinsic Value	$ 192,800		$ 56,844
Average Intrinsic Value, Vested and expected to vest	156,604
Average Intrinsic Value, Exercisable	$ 88,612
Weighted Average Exercise Term, Outstanding Balance	8 years		8 years 3 months 15 days
Weighted Average Exercise Term, Vested and expected to vest	7 years 10 months 2 days
Weighted Average Exercise Term, Exercisable	7 years 5 months 12 days